Microphone.



G. A. NUSSBAUM.

MICROPHONE.

APPLICATION FILED MAY 4 1912.

1,069,899.. Patented Aug. 12, 1913.

Wiinencr,

MM Zia 1 fliiorney vtliieemlt or tennoni n e wn DEGEQEHQNE.

Specification of Le tter s Patent.

Patented Au 312, 11ers.

, Application filed May a, 1912. Serial in. 695,225.

To all whom, it may concern:

Be it known that l, GUIILAUMJE ARNAUD NUSSBAUM, a subject of the King of Great Britain and Ireland, residing in the city of London, England, have invented Improvements in Microphones, of which the following-is a specification.

This invention, which relates to microphones, has for its object to secure increased eiliciency by providing that the carbon granules shall be confined circumferentially between conducting-plates or diaphragzns by a wall that, in contradistinction to the walls heretofore employed, is of a highly resilient character, being for this purpose made hollow and easily deformed laterally so that every diaphragm fluctuation produces a very material alteration in the area circumscribed by the inner surface of the wall, with the result that the granules are subject to disturbing motions at right angles to one another as each sound wave occurs, thereby effectually preventing packing of the granu es. 7

In the accompanying drawings, Figure l is a section of a microphone embodying the invention. Fig. 2 is a plan corresponding to Fig. 1 but with parts removed. Figs. 3

and 4: are similar views of a modified diaphragin arrangement.

In Figs. 1 and 2, a is the mouthpiece and b the front part and c the rear part of the casing of the microphone. cl is the hup insulated from the casing part c and containing the carbon granules e, and the rear electrode f, g is the vibrating diaphragm. The diaphragm 9 may be held in position in the casing in any well known or suitable way, being shown as supported between a tubular metal ring 71 and a tubular ring 5 of india rubber or like yielding material.

The carbon granules e are, according to the invention, surrounded by a tubular ring 7' of resilient material such as india rubber tubing, of appropriate cross section, in the example circular, hermetically sealed. This ring 7' is fixed or held more or less centrally against the rear electrode f, as for example by the wall of thecup d which acts to resist deformation in an outward direction and enhance the inward thrust upon the granules when thetube is flattened. The diaphragm g is made to bear lightly against the ring lhe sound waves acting on the diaphragm 9 more or less depress the ring 7', so that simul- 5 taneously with diminution of the distance between the diaphragm g and rear electrode ,1 there is an inward motion of the inner peripheral portion of the ring which produces a reliable pressing together of the carbon granules and on the I diaphragm moving away from the rearelectrode, the pressure on the ring is reduced so that the inner peripheral portion thereof movesoutward and lessens the pressure on the granules. In this way the resistance of the microphone is found to vary in a very eilicient manner and packing of the granules prevented.

llnstead oi using only one diaphragm,

= there may, as shown in Fig. 3, be employed 7 0 two diaphragms 70, m, these being shown as separated by an insulating washer n (Figs.

3 and a), while the granules e are confined by the tubular j of the invention, the said ring in this case being attached, as by adhesive, to one or to both of, the diaphragms. With this type of microphone the sound waves act on both diaphragms.

What I -claim is l. A microphone comprising two juxta-to posed conducting plates one at least of which is adapted to constitute a vibratory diaphragm, a hollow hermetically sealed pneumatic ring of impervious elastic material, as india rubber, held between said plates and the inner periphery of which is free to expand inward, a rigid surrounding support for the outer periphery of the ring and conducting granules filling the space confined between the plates and ring and in contact with the latter.

2. A microphone comprising a casing, a vibratory diaphragm held at its periphery in said casing, a cup carried by said casing,

a rear electrode held within-said cup the wall of which extends beyond said rear electrode toward the diaphragm, a hermetically sealed hollow pneumatic ring of india rubber held within said cup between said diaphragm'and rear electrode so that its inner periphery is free to expand inward while its outer periphery is prevented fromexpanding'outward' by the extended wall of said cup, and conducting granules filling the space confined between thediaphragm, rear electrode and inner peripheryof said ring and in direcvcontact .with the latter.

Signed atLondon England this 23rd day of April 1912.

7 HERBERT D. J nson. 

